Hi folks. I'm hoping I can occupy a few minutes of your time. I'm not a student or scientist, I'm a writer doing research for my first novel. I know this post is broad and possibly confusing, and I apologize in advance for it.

I'll try to keep this brief. In my novel, in the distant future, a group of 5,000 to 10,000 colonists have settled a new planet and separated from Earth entirely. Over the next thousand years, they spend their time in an environment which is slightly different from ours, here and there--perhaps a bit more nitrogen in the atmosphere, perhaps a bit less ultraviolet light to contend with.

After that thousand years, they return to Earth looking and functioning with a notable difference in culture and physiology (the latter being the subject of my post), from adapting to a different environment over a relatively short amount of time. They also have genetic engineering capabilities, and purposefully alter their physiological makeup to cope with the environment.

If we lived a thousand years on a planet with these small changes--and any other possible causes that you could imagine would effect humans so as to cause significant changes, including genetic engineering--what would you *speculate* both the causes and effects could be? I'm looking for a mechanism by which humans would return a thousand years later with altered--and advantageously so--physiology.

This is a brainstorm experiment, and your input would be very much appreciated. Let me know if and how I can improve my post. Thank you for your time and sorry for the possibly confusing question.

To summarize: I need a mechanism by which humans could be physiologically altered (mostly in an advantageous way) over a relatively short period of time. And I'm curious as to what the effects of small changes in environment could be after a thousand years.

A thousand years (~50 generations) is not much time for significant genetic adaptation to take place. For example, there was a recent study on the adaptation of Tibetans to high altitude, estimating it to have taken about 3000 years - which if true, is surprisingly fast. The more hardship a population is under, in terms of fraction of lives lost per generation (Tibet is, of course, a very harsh environment), the more drastic the change can be. Small differences in environment may not lead to any noticeable change at all.

However, there will also be environmental factors to consider (since the human body can adapt without genetic change). These changes would be at least partially reversible if they return to our environment (although it might take several years), while the genetic ones would not. I imagine that you would probably have to explain this to your readers at some point. The effects of genetic and environmental factors will be mainly in the same direction - so the longer time there is, the more change could occur - environmental change shifts your location on the spectrum of possible physiology for a given genetic background, and genetic change shifts the position of that spectrum. If they have technology to resist the environment (like if they make and use pressurized oxygen, or the ability to save the lives of people who would otherwise die from lack of oxygen), the impact will be softened or eliminated.

The environmental effects of having less oxygen should be similar to what we see when someone is born to parents with genetics from a low altitude, but is raised and lives at a high altitude. So they will probably have more red blood cells, a stronger diaphragm, a stronger heart, etc. This would allow them to (for example) exert themselves for longer under our conditions (but they could only act normally under theirs, because the extra adaptations are a compensation for the environment). Any of our people who go to their conditions won't have those compensating factors, and might (or might not, depending on the amount of difference, and what their background is on Earth) find it hard to breathe and exert themselves.

It would be extremely unlikely for any completely new traits to arise, unless they engineered it. So any non-engineered genetic change you want in your new population should be present to at least some degree in the founding population. Based on the study I mentioned, if you start with people from sea level, then given conditions of hardship I would take the physiology of present-day Tibetans as a maximum for the sum of (non-engineered) genetic and environmental change over the 1000 years. Although if your starting population is (for example) Tibetan, then you are talking about the variation within their population and not the general population. And perhaps you might be willing to give them more than a thousand years.

I don't think there's anything major that would come as an adaptation to UV exposure - probably a lower rate of skin cancer and eye damage, and probably lighter skin. Until the lighter skin comes along, they will suffer from partial Vitamin D deficiency.

Anyways, this post is probably too long now - someone else will probably tell me if I've missed anything. I recommend David Weber's Honor Harrington books, if you haven't read them - if I recall correctly, the people of Grayson were isolated for about a thousand years in a harsh environment with a high death rate. The culture changed extremely fast, but I think the major genetic change (different sex ratio) was actually due to making a mistake during the genetic engineering.

Agree with astra, there might be phenotypic plasticitymtoward adaptation but probably not much genetic change, esp. as you've offered no selective element in your scenario. You might explore some social factor for selection in breeding that drives change more rpidly. What is the motivation for "genetic engineering" in the scenario? Like central planning in economics, it sounds good but probably doesn;t work ut so well.